Method for sweetening petroleum distillates



Patented Aug. 21, 1951 UNITED STATES PATENT OFFICE METHOD FORSVVEETENING PETROLEUM DISTILLATES John G. Browder, Houston, and Alvin R.Smith,

Baytown, Tex., assignors, by mesne assignments, to Standard OilDevelopment'Company, Elizabeth, N. J a corporation of Delaware NoDrawing. Application September 12, 1949, Serial No. 115,311

aqueous alkaline solutions, such as solutions of alkali metal hydroxide,to remove hydrogen sulfide and other acidic bodies, following which thesour distillates were treated withsodium plumbite solution to convertdeleterious sulfur compounds to compounds which are largely innocuous.This and other prior art processes relied on the addition of sulfur tocause the conversion of the sulfur compounds from mercaptans todisulfides. Other processes convert the undesirable compounds by meansof lead sulfide, which is then separated from the gasoline. Frequently,the separation of lead sulfide from the gasoline was not complete, and,consequently, some was carried over into storage, which wasdisadvantageous. Furthermore, the addition of sulfur to gasolinefrequently impaired the octane number level of the gasoline since it iswell known that sulfur and its compounds affect gasoline detrimentally.

Efforts have been made in the prior art to remedy this situation, andthe workers in the field have turned to adding certain compounds, suchas phenols and amines, to alkaline solutions, such as sodium hydroxidatocause conversion through an oxidation mechanism of the deleteriouscompounds in the sour naphtha. Frequently such expedients areunsatisfactory in not completely sweetening the product, and anafter-treatment, by one of the well known sweetening procedures, becomesnecessary.

It has also been known, in the prior art, to employ alcohols in anon-oxidative sweetening process in which small quantities of alcoholare added to the solutions of sodium hydroxide and to the petroleumdistillate being sweetened to extract mercaptans from the sourhydrocarbons. In such processes the alcohol is either used ,as aqueousalcohol dissolved in the alkali metal hydroxide, or the alcohol is addedto the caustic solution in large concentrations to provide a solentwhich will remove the mercaptans in solution. Thus the prior artteachings have been to the effect in the employment of substantiallyanhydrous alcohol in conjunction with caustic or in the employmentof-alcohol in non-oxidative sweetening processes. Such art, on the face,would appear disadvantageous in obtaining a sweetened product inrequiring expensive equipment in view of using large amounts of solventor in not completely sweetening the product.

From the foregoing discussion of theprior art, it will be seen that thepetroleum refining industry has been faced wtih a problem of convertingdeleterious sulfur compounds present in petroleum distillates to thosewhich do not detrimentally affect the quality of the product.

It is therefore the main object of the present invention to provide atreating process in which improved results are obtained in convertingobjectionable sulfur compounds to harmless bodies.

Another object of the present invention is to provide an improvedsweetening process in which an active material is added to the petroleumdistillate being sweetened to catalyze the conversion of deleterioussulfur compounds.

Another object of the present invention is to provide an improvedsweetening process in which small amounts of catalytic reagents areemployed.

In the foregoing discussion of the prior art, it will be seen that theprior workers in this field have employed compounds such as phenol,amines and alcohols in sweetening processes in which alkaline solutionswere used to treat sour naphthas. proved results may be obtained inoxidative sweetening processes in which an alkali metal hydroxide isemployed by adding a catalytic amount of pyridine to the sour distillatewhich is to be sweetened. Thus, in accordance with the present inventionthe foregoing objects may be achieved by adding pyridine to a sourpetroleum distillate and then contacting the sour distillate to whichpyridine has been added with a catalytic amount of a solution of analkali metal hydroxide while maintaining in contact therewith a mildoxidizing agent.

Accordingly, the present invention may be described briefly as involvingcontacting a sour We have now found that im-' petroleum distillatehaving a boiling range of about 50 to 750 F. to which has been added asmall amount of pyridine in catalytic quantity with a solution of analkali metal hydroxide to form a mixture thereof and maintaining themixture undergoing contacting in the presence of a mild oxidizing agentin an amount suificient to sweeten said distillate, following which thealkali metal hydroxide is separated from the contacted distillates.

The pyridine may be employed in amounts based onthe sour distillatevarying from 0.1 to 5% by volume, with a preferred range of about 0.5 to1% by volume. The pyridine is preferably added to the petroleumdistillate, but may be added to the mixture of the alkali metal hydrox-.I

ide and sour petroleum distillate undergoing the sweetening reactions.

The alkali metal hydroxide employed in the present invention preferablyshould be a solution of an alkali metal hydroxide. Preferably thesolution should be an aqueous solution having a Baum gravity in therange of from about to about 50 Baum, but solutions of lower strengthmay be used under some conditions. An aqueous solution of. sodium,hydroxide of Baum has been found to give satisfactory results, inthepractice. of the present invention. Other alkali metal hydroxidesbesides sodium hydroxide may be; used, For example, lithium, and

potassium hydroxides, may beused, in lieu of so.- dium hydroxide, butthe latter is to be preferred.

The temperature at which the treating operation, is conducted willusually be atmospheric temperature and may range from, about (it:

up to, ZQQ- E. and sometimes. higher temperatures may, be,employeddepending on the boiling range apdthetype of feedstock, beingtreated. A preferred temperature range may be from about 7 0, to about,95 F. Satsifactory results have been obtained. at atmospherictemperatures encpuntered-inthe 'I-exaSGnlf Coast area.

The process. of. our invention may be carried.

out. in suitable equipment which will allow contact of; the sourdistillate to which pyridine has-v been added with the alkali metalhydroxide and the mild oxidizing agent, For example, pumps, jet mixers,incorporators and contacting towers may. be used. Such towersmay beequipped with packing, bell cap trays and, other similar well known;expedients, for insuring contact between liquids, and between liquidsand gaseous material.

The, present, invention will be illustrated furhe y. the p ow n xamp e:

EXAMPLE I it sour petroleum distillate boiling in the 350 to 540? Iboiling range was divided into two portions; one portion was contacted,with a Baum; sodium hydroxide solution in the presence of 3 0Q or thetheoretical amount of oxygenrequired to. sweeten said sour distillate.The e on pbrti riv had add d o. i 0.5% Of py dine and was likewisecontacted with a solution.

of sodium hydroxide having a. Baum gravity Qt 50. After the contactingoperation, the so dium hydroxide solution was separated from thecontacted distillate and the copper number of,

information with, regard to the contacting operation are presented inthe table which follows:

Table Treatment:

50 B. caustic, per cent 1.0 1.0 Oxygen, per cent of theoretical 300 300Pyridine, per cent 0.5 Copper No. before treat 65 65 Copper No. aftertreat: Immediately after. 49 1 hour after 29 6 3 hours after 17 5 hoursafter 15 6 20 hours after 10 3 From the foregoing data it will beapparent that the copper number of the distillate without the additionof pyridine was lowered from to 10 after 20 hours setting time. On theother hand, the copper number of the distillate to which pyridine was.added was reduced to 6 one hour after the treatment had been concludedand toy 3 after twenty hours settling time.

In the foregoing example, the improvement obtained by the practice ofthe present invention has been illustrated by the copper number test.This is a Well known analytical procedure in the petroleum industry. Adescription of the method of test may be found in U. 0. P. LaboratoryTest Methods for Petroleum and Its Products,"

third edition, page H61, Universal Oil Products Co., Chicago, 1947. Thistest is a measure of the mercaptan sulfur content of the oil beingtested.

Although not illustrated by the several exsary to replace the entrainedamount with fresh- 5 solution. In short, it is contemplated in thepractice of the present invention that the alkali metal hydroxidesolution will be reused over and over again since it is not necessary toregenerate the alkali metal hydroxide solution.

The invention has been described and illustrated by employment of a mildoxidizing agent such as oxygen. It is contemplated thatmixtures ofoxygen with other gases, such as air-may be employed. It is alsocontemplated that other mild oxidizing agents such as peroxides,permanganates, and the like may be used, For example, a hydrogenperoxide solution may be em.- ployed as the mild' oxidizing agent.

In practicing the present invention, it is to be understood that thepetroleum distillate may be. subjected to a preliminary treatment forre,- moval of hydrogen sulfide if the distillate contains hydrogensulfide. Such. preliminaryv treat.- ment may include washing with adilute. alkali metal hydroxide solution or blowingv with a freeoxygencontaining gas such as air. sulfide or other acidic compounds arepresent and not removed, the alkali metalhydroxide solu-- tion employedasthe catalyst may very. quickly become seriously depleted in activity.

In the practice of the invention, it will be d6.-

sirable to use. an amount of oxygen in excess. of,

the theoretical required tosweeten the, sour petroleum distillate.Ordinarily,

amples, one of the particular advantages ofthe If hydrogen,

an amount of.

about 300% of the theoretical amount to sweeten may be employed.However, sweetening in accordance with the present invention may beobtained with considerably lesser quantities of oxygen. In otherinstances as much as 500% of the theoretical amount required to sweetenmay be employed. In fact, sweetening may be obtained in some cases bycontact with the oxygen present in the treating vessel. It will bedesirable to employ an amount of oxidizing agent at least equivalent tothe theoretical amount required to sweeten.

The invention has been described and exemplified by employment of 0.5 to1% by volume of the catalytic alkali metal hydroxide solution. It iscontemplated that as little as 0.1 and as much as 5% by volume, or more,of the alkali metal hydroxide solution, based on the sour naphtha, maybe employed. Very good results, however, are obtained with 1% by volumeand this amount will be preferred.

It is to be understood that after separation of the alkali metalhydroxide solution the contacted naphtha may be washed with water, ifdesired, to remove any alkali metal hydroxide which may be entrainedtherein, although in most instances it will be unnecessary to treat thecontacted naphtha with water or other aqueous solutions.

The nature and objects of the present invention having been completelydescribed and illustrated, what we wish to claim as new and useful andto secure by Letters Patent is:

1. A method for sweetening a sour petroleum distillate which comprisescontacting a sour petroleum distillate boiling below 750 F. with asolution of an alkali metal hydroxide in the presence of pyridine and amild oxidizing agent to obtain a sweetened distillate, said alkali metalhydroxide being present in an amount in the range of 0.1% to 5.0% byvolume based on the sour petroleum distillate and said pyridine beingpresent in an amount in the range of 0.1% to 5.0% by volume based on thesour petroleum distillate.

2. A method for sweetening a sour petroleum distillate boiling below 750F. which comprises adding to said distillate an amount of pyridine inthe range from 0.1 to 5% by volume based on said distillate, forming amixture of an aqueous solution of an alkali metal hydroxide and saidsour petroleum distillate to which pyridine has been added, andagitating the mixture in the presence of a mild oxidizing agent toobtain a sweetened distillate, said solution of alkali metal hydroxidebeing present in the mixture in an amount in the range of 0.1% to 5.0%by volume based on the sour petroleum distillate.

3. A method for sweetening a sour petroleum distillate boiling below 750F. which comprises adding to said distillate an amount of pyridine inthe range from 0.1 to 5% by volume based on said distillate, forming amixture of an aqueous solution of sodium hydroxide and said sourpetroleum distillate to which pyridine has been added, the aqueoussolution or" sodium hydroxide being present in the mixture in an amountin the range of 0.1% to 5.0% by volume based on the sour petroleumdistillate, agitating the mixture in the presence of air to causesweetening of said distillate, separating sodium hydroxide solution fromsaid distillate and recovering said distillate.

4. A method for sweetening a sour petroleum distillate which comprisesadding 0.5% by volume of pyridine to said sour petroleum distillate,forming a mixture of said sour petroleum distillate to which pyridinehas been added with an aqueous solution of sodium hydroxide having aBaum gravity of A. P. I., the aqueous solution of sodium hydroxide beingpresent in the mixture in an amount in the range of 0.1% to 5.0% byvolume based on the sour petroleum distillate, agitating the mixture inthe presence of air to cause sweetening of said distillate, separatingsaid sodium hydroxide solution from said agitated distillate, andrecovering said agitated distillate.

5. A method in accordance with claim 4 in which the amount of sodiumhydroxide solution is 1% by volume based on the sour distillate.

JOHN G. BROWDER. ALVIN R. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS (2nd addition to No. 827,345)

1. A METHOD FOR SWEETENING A SOUR PETROLEUM DISTIALLATE WHICH COMPRISESCONTACTING A SOUR PETROLEUM DISTILLATE BOILING BELOW 750* F. WITH ASOLUTION OF AN ALKALI METAL HYDROXIDE IN THE PRESENCE OF PYRIDINE AND AMILD OXIDIZING AGENT TO OBTAIN A SWEETENED DISTILLATE, SAID ALKALI METALHYDROXIDE BEING PRESENT IN AN AMOUNT IN THE RANGE OF 0.1% TO 5.0% BYVOLUME BASED ON THE SOUR PETROLEUM DISTILLATE AND SAID PYRIDINE BEINGPRESEENT IN AN AMOUNT IN THE RANGE OF 0.1% TO 5.0% BY VOLUME BASED ONTHE SOUR PETROLEUM DISTILLATE.